Control apparatuses for a synchronous rotary electric machine perform field-weakening control that aims to increase the rotational speed of the synchronous rotary electric machine while keeping torque of the synchronous rotary electric machine to a constant value. The field-weakening control decreases a d-axis current, which is flowing through an armature coil of the synchronous rotary electric machine.
In addition, control apparatuses for a wound-field rotary electric machine perform field flux control that aims to increase the torque of the wound-field rotary electric machine. The field flux control increases a field current, which is flowing through a field winding of the wound-field rotary electric machine, to thereby increase a magnetic field.
For example, a control apparatus for a wound-field rotary electric machine may perform both the field-weakening control and the field flux control. This changes the d-axis current, and the change of the d-axis current may result in a disturbance voltage being induced in the field winding due to magnetic coupling between the field winding and the armature coil. This disturbance voltage may cause the field current to fluctuate.
Similarly, execution of both the field-weakening control and the field flux control changes the field current, and the change of the field current may result in a disturbance voltage being induced in the armature coil. This disturbance voltage may cause the d-axis current to fluctuate.
These field-current and d-axis-current changes may result in torque of the wound-field rotary electric machine fluctuating. In particular, the inductances of field windings have been becoming lower in recent years in order to achieve higher torque response. This may cause fluctuations of the field current due to the disturbance voltage to have a significant impact on the torque of the wound-field rotary electric machine.
For reducing torque variations due to the disturbance voltage, a conventional control apparatus, which is disclosed in patent literature 1, is configured to correct a command value for the field current in accordance with the amount of change of the d-axis current.